The present invention relates to a method for manufacturing glass fiber-reinforced resin moldings, and particularly to a method for manufacturing glass fiber-reinforced resin moldings in which glass fibers are uniformly dispersed.
A glass fiber reinforced resin, which is prepared by mixing glass fibers with a thermoplastic resin, can be significantly improved in strength, modulus, impact resistance, heat resistance, and the like, and therefore, such a resin is used for various plastic products. The kind of resin with which glass fibers are mixed is extended in a wide range from a general purpose resin such as polypropylene or a styrene based resin to an engineering plastic such as nylon, polycarbonate, PBT, or PET.
Glass fibers used for this purpose are called chopped strands formed by forcibly bonding several hundreds of glass fibers of about 10 xcexcm in diameter to each other with a binder such as epoxy resin, polyurethane, or acid-modified polypropylene. If the bonding strength is weak, during the mixing of the chopped strands with resin pellets, the chopped strands are split into flake-like fibers similar to cotton waste to be increased in volume, and thereby they are not uniformly mixed with the resin. Accordingly, since the bonding strength must be stronger, the above-described resin component as the binder is required to be used in an amount of 1% or more. A molded body, characterized in that glass fibers are uniformly dispersed by incorporating such chopped strands in a resin, has been produced by a manner of heating and kneading a mixture of a raw resin and glass fiber chopped strands by an extruder to melt the resin, extruding the fiber mixed resin to prepare resin pellets in which glass fibers are uniformly dispersed, followed by feeding these pellets in an injection molding machine, heating and kneading the pellets inside the molding machine to melt the resin, and injecting the fiber mixed resin into a mold to obtain a molded body of a desired shape. Such two-stage production method, however, is disadvantageous in that not only the production cost becomes higher but also mechanical properties of the molded body may be degraded because of a phenomenon that glass fibers are rubbed with a wall surface of the molding machine or manually rubbed to be scratched or damaged.
Incidentally, if a mixture of a thermoplastic resin and glass fibers is injection molded in one stage by using only a general injection molding machine, there may occur an inconvenience that bundles of the glass fibers are liable to be formed in a molded body because of poor dispersion of the glass fibers, to cause irregularities on the surface of the molded body, with a result that not only the appearance of the molded body becomes poor but also portions in which the bundles of the glass fibers are present are weakened in strength to be easily cracked.
To improve the above inconvenience, for example, Japanese Patent Publication No. Sho 56-47847 proposes an injection molding machine additionally provided with a kneading mechanism for dispersing glass fibers, in which kneading and injection molding are simultaneously performed by making use of such a kneading mechanism.
The use of the above-described molding machine, however, is insufficient yet to uniformly disperse glass fibers, and also causes a problem that since a mixture of a resin and glass fibers is mechanically, strongly kneaded, glass fibers may be finely broken, thereby failing to sufficiently achieve the reinforcing function of the glass fibers. Another problem lies in significantly increasing the apparatus cost because of provision of such a special kneading mechanism, to raise the production cost, leading to an economical disadvantage.
In view of the foregoing, the present inventors have earnestly studied, and found that the addition of a peroxide to a thermoplastic resin makes it possible to obtain a molded body of the resin in which glass fibers are uniformly dispersed and also to easily produce a molded body of the resin in which glass fiber are uniformly dispersed by using a general purpose injection molding machine, and on the basis of such knowledge, the present inventors have accomplished the present invention.
An object of the present invention is to provide a method for manufacturing glass fiber-reinforced resin moldings, which is capable of uniformly dispersing, glass fibers in a resin and obtaining a molded body having an excellent appearance.
The present invention provides a method for manufacturing glass fiber-reinforced resin moldings including the step of manufacturing glass fiber-reinforced resin moldings by using a molding material prepared by mixing glass fibers with a thermoplastic resin, characterized in that a peroxide is added to the molding material to be molded.
Examples of thermoplastic resins as the raw resins used in the present invention may include polypropylene, polyethylene, a styrene based resin such as SAN or ABS, and nylon.
Glass fibers are added to a resin for improving the strength and elasticity of a molded body. As glass fibers used in the present invention, there can be used glass fibers generally used for manufacturing glass fiber-reinforced resin moldings of this type.
A peroxide added to a molding material may be either an organic peroxide or an inorganic peroxide. In the case of adding an organic peroxide, the content thereof may be in a range of 0.01 to 0.5 wt % on the basis of the amount of the thermoplastic resin.
According to the present invention, a molded body may be produced by either injection molding or extrusion molding. That is to say, the present invention can be applied to both the molding processes. The method of the present invention, which is applied, for example, to injection molding, will be described below. First, a thermoplastic resin, glass fibers and a peroxide are heated and kneaded in an injection molding machine, to uniformly disperse the glass fibers in the resin by the function of the peroxide. Then, the glass fiber mixed molten resin in which the glass fibers are uniformly dispersed is injected in a mold through a nozzle until the mold is filled therewith, to obtain a desired molded body.
According to the present invention, since in manufacturing glass fiber-reinforced resin moldings by using a molding material prepared by mixing glass fibers with a thermoplastic resin wherein a peroxide is added to the molding material to be molded, the glass fibers are uniformly dispersed in the resin by the function of the peroxide, to obtain a molded body having an excellent appearance. In addition, although the peroxide is added to the resin, the physical properties of the resin are not reduced and the desired physical properties of the resin can be ensured.
According to the present invention, since the uniform dispersion of glass fibers can be obtained, in the case of applying the present invention to injection molding, it is possible to eliminate the necessity of provision of a special kneading mechanism for uniformly dispersing glass fibers. Accordingly, there can be obtained an effect of adopting a conventional injection molding machine, to reduce the production cost, thereby achieving an economical advantage.
Further, according to the present invention, since the uniform dispersion of glass fibers in a resin is performed in an injection molding machine, it is possible to eliminate the necessity of adopting a two-stage production method in which resin pellets in which glass fibers are uniformly dispersed are once prepared by an extruder, and a molded body is produced by an injection molding machine by using the resin pellets. Accordingly, the present invention exhibits an effect of obtaining a molded body with a high quality in one stage by using only an injection molding machine, to reduce the number of steps, thereby lowering the production cost.